PRESSURE

Photo by: fabioberti.it

Pressure is the ratio of force to the surface area over which it is
exerted. Though solids exert pressure, the most interesting examples of
pressure involve fluids—that is, gases and liquids—and in
particular water and air. Pressure plays a number of important roles in
daily life, among them its function in the operation of pumps and
hydraulic presses. The maintenance of ordinary air pressure is essential
to human health and well-being: the body is perfectly suited to the
ordinary pressure of the atmosphere, and if that pressure is altered
significantly, a person may experience harmful or even fatal
side-effects.